There has hitherto been used semiconductor acceleration sensors disposed in a vehicle or tire of an automobile for performing vehicle posture control or sensing a distortion of the tire.
One example of this sort of semiconductor acceleration sensor will be described with reference to FIGS. 21 to 23. FIG. 21 is an external perspective view; FIG. 22 is a cross-sectional view observed from the arrow direction along the line A-A shown in FIG. 21; FIG. 23 is a cross-sectional view observed from the arrow direction along the line B-B shown in FIG. 21. As shown in FIG. 21, the semiconductor acceleration sensor 20 includes a pedestal 21 having a rectangular frame shape and is constituted of a silicon substrate 22 mounted on one opening plane of the pedestal 21.
Also, in the center of the silicon substrate 22 corresponding to the opening of the pedestal 21, there is formed a diaphragm 23 of thin film having a cross shape; on the upper surface of each of the diaphragm pieces 23a to 23d, there is formed a piezo resistor 26. Further, on one surface side of the center of the diaphragm 23 in the crossing section of the diaphragm pieces 23a to 23d, there is formed a thick film section 24; on the surface of the thick film section 24, there is mounted a plumb bob 25 having a rectangular solid shape made of, for example, glass.
In the semiconductor acceleration sensor 20 having the above described configuration, when force generated in association with acceleration is exerted on the plumb bob 25, distortion occurs in each of the diaphragm pieces 23a to 23d, whereby the resistance value of the piezo resistor 26 varies. Accordingly, with the resistor bridge circuit formed with the piezo resistor 26 arranged in each of the predetermined diaphragm pieces 23a to 23d, accelerations can be sensed in predetermined directions, e.g., in X axis, Y axis and Z axis directions orthogonal to each other.
As an example of the semiconductor acceleration sensor described above, there has been known semiconductor acceleration sensors disclosed in Japanese Patent Publication Nos. H8-75775 and 2000-28633.
Japanese Patent Publication No. H8-75775
Japanese Patent Publication No. 2000-28633.